/*========================== begin_copyright_notice ============================

Copyright (C) 2022 Intel Corporation

SPDX-License-Identifier: MIT

============================= end_copyright_notice ===========================*/

#include "Compiler/CodeGenPublic.h"
#include "Compiler/CISACodeGen/SinkCommonOffsetFromGEP.h"
#include "Compiler/CISACodeGen/ShaderCodeGen.hpp"
#include "Compiler/IGCPassSupport.h"
#include "llvm/IR/DerivedTypes.h"
#include <vector>
#include <algorithm>

using namespace llvm;
using namespace IGC;

namespace {
// This is to sink to the successor block the common constant offset from several GEP
// e.g
// ************************************
// bb1:
//    %0 = gep(a, 0)
//    %1 = gep(a, 1)
// bb2:
//    %2 = gep(b, 0)
//    %3 = gep(b, 1)
// bb3:
//    %4 = phi( [%0, bb1], [%2, bb2] )
//    %5 = phi( [%1, bb1], [%3, bb2] )
//    load [%4]
//    load [%5]
// ************************************
//
// converts to
//
// ************************************
// bb1:
//    %0 = a
// bb2:
//    %1 = b
// bb3:
//    %2 = phi( [%0, bb1], [%1, bb2] )
//    %3 = gep(%2, 0)
//    %4 = gep(%2, 1)
//    load[%3]
//    load[%4]
// ************************************
// This have two goals:
// 1) Could decrease register pressure
// 2) The MemOpt pass will merge loads

class SinkCommonOffsetFromGEP : public llvm::FunctionPass {

public:
  static char ID;

  SinkCommonOffsetFromGEP();
  virtual bool runOnFunction(llvm::Function &F) override;

  virtual void getAnalysisUsage(llvm::AnalysisUsage &AU) const override { AU.setPreservesCFG(); }
};

// Struct for save GEP and corresponding addrespace cast instruction if exist
struct GepPointer {
  GetElementPtrInst *GEP;
  AddrSpaceCastInst *Cast;

  static GepPointer get(Value *V);
};

// Struct for save divergent pointer phi node and corresponding GEP instructions
struct DivergentPointer {
  PHINode *Phi = nullptr;
  MapVector<BasicBlock *, GepPointer> Geps;

  static DivergentPointer create(PHINode *PN);
};

// CommonBaseGroup is aimed to save all divergent pointers with common base of GEP
// e.g:
//
// bb1:
//   %0 = gep(a1, 0)
//   %1 = gep(a1, 1)
//
//   %3 = gep(a2, 0)
//   %4 = gep(a2, 1)
// bb2:
//   %5 = gep(b1, 0)
//   %6 = gep(b1, 1)
//
//   %7 = gep(b2, 0)
//   %8 = gep(b2, 1)
//
// CommonBaseGroupArray[0] = { { %0, %5}, {%1, %6} }
// CommonBaseGroupArray[1] = { { %3, %7}, {%4, %8} }
struct CommonBaseGroup {
  SmallVector<DivergentPointer, 2> DivergentPointers;
  MapVector<BasicBlock *, std::pair<std::pair<Type *, Value *>, SmallVector<Value *, 4>>> GroupFactor;
  MapVector<BasicBlock *, AddrSpaceCastInst *> Casts;
  BasicBlock *Successor = nullptr;
};

class DivergentPointersGroups {
public:
  DivergentPointersGroups() = default;

  void add(const DivergentPointer &DP);
  const std::vector<CommonBaseGroup> &getGroups() const { return PointerGroups; }

private:
  std::vector<CommonBaseGroup> PointerGroups;

  bool addToExistingGroup(const DivergentPointer &DP);
  bool createAddNewGroups(const DivergentPointer &DP);
  static bool isBelongedToGroup(const CommonBaseGroup &Group, const DivergentPointer &DP);
};

} // End anonymous namespace

char SinkCommonOffsetFromGEP::ID = 0;

#define PASS_FLAG "igc-sink-gep-constant"
#define PASS_DESCRIPTION "IGC Sink Common Offset From GEP"
#define PASS_CFG_ONLY false
#define PASS_ANALYSIS false

namespace IGC {
IGC_INITIALIZE_PASS_BEGIN(SinkCommonOffsetFromGEP, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
IGC_INITIALIZE_PASS_END(SinkCommonOffsetFromGEP, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
} // namespace IGC

FunctionPass *IGC::createSinkCommonOffsetFromGEPPass() { return new SinkCommonOffsetFromGEP(); }

SinkCommonOffsetFromGEP::SinkCommonOffsetFromGEP() : FunctionPass(ID) {
  initializeSinkCommonOffsetFromGEPPass(*PassRegistry::getPassRegistry());
}

GepPointer GepPointer::get(Value *V) {
  GepPointer GP{nullptr, nullptr};

  Value *CurV = V;
  if (auto ASC = dyn_cast<AddrSpaceCastInst>(CurV)) {
    GP.Cast = ASC;
    CurV = ASC->getPointerOperand();
  }

  GP.GEP = dyn_cast<GetElementPtrInst>(CurV);
  return GP;
}

// Create DivergentPointer for phi node. If cannot find GEP for any incoming value Phi field is nullptr
DivergentPointer DivergentPointer::create(PHINode *PN) {
  DivergentPointer DP;
  for (Use &IV : PN->incoming_values()) {

    auto GP = GepPointer::get(IV.get());
    if (GP.GEP == nullptr)
      return DP;

    DP.Geps[PN->getIncomingBlock(IV)] = GP;
  }

  DP.Phi = PN;
  return DP;
}

// Get pure pointer skipping the cast operations
static Value *getPointer(Value *V) {
  if (auto ASC = dyn_cast<AddrSpaceCastInst>(V))
    return getPointer(ASC->getPointerOperand());
  if (auto BC = dyn_cast<BitCastInst>(V))
    return getPointer(BC->getOperand(0));
  return V;
}

// Get pointer for load/store
static Value *getPointerForMemRef(Instruction *I) {
  Value *Pointer = nullptr;
  if (auto LD = dyn_cast<LoadInst>(I))
    Pointer = getPointer(LD->getPointerOperand());
  if (auto ST = dyn_cast<StoreInst>(I))
    Pointer = getPointer(ST->getPointerOperand());

  return Pointer;
}

static std::vector<DivergentPointer> findDivergentPointers(BasicBlock *BB) {
  std::vector<DivergentPointer> DivergentPointers;
  for (auto II = BB->begin(), IE = BB->end(); II != IE; ++II) {

    Instruction *I = &(*II);

    if (!isa<LoadInst>(I) && !isa<StoreInst>(I))
      continue;

    auto Pointer = getPointerForMemRef(I);
    if (Pointer == nullptr)
      continue;

    auto PhiPointer = dyn_cast<PHINode>(Pointer);
    if (PhiPointer == nullptr)
      continue;

    auto DP = DivergentPointer::create(PhiPointer);
    if (DP.Phi == nullptr)
      continue;

    DivergentPointers.push_back(DP);
  }
  return DivergentPointers;
}

// Check if current DivergentPointer belonng to any CommonBaseGroup
bool DivergentPointersGroups::isBelongedToGroup(const CommonBaseGroup &Group, const DivergentPointer &DP) {
  DenseMap<BasicBlock *, std::pair<Value *, SmallVector<Value *, 4>>> CurGroupFactor;

  for (auto &IT : DP.Geps) {
    BasicBlock *BB = IT.first;
    GetElementPtrInst *GEP = IT.second.GEP;

    auto PtrOperand = GEP->getPointerOperand();
    SmallVector<Value *, 4> BaseIndices(GEP->idx_begin(), GEP->idx_end() - 1);
    CurGroupFactor[BB] = std::make_pair(PtrOperand, BaseIndices);
  }

  BasicBlock *Successor = DP.Phi->getParent();
  if (Successor != Group.Successor)
    return false;

  for (auto &IT : Group.GroupFactor) {
    BasicBlock *BB = IT.first;
    Value *PtrOperand = IT.second.first.second;
    auto &Indices = IT.second.second;

    if (CurGroupFactor[BB].first != PtrOperand)
      return false;
    if (CurGroupFactor[BB].second != Indices)
      return false;
  }
  return true;
}

bool DivergentPointersGroups::addToExistingGroup(const DivergentPointer &DP) {
  for (auto &Group : PointerGroups) {
    if (isBelongedToGroup(Group, DP)) {
      Group.DivergentPointers.push_back(DP);
      return true;
    }
  }
  return false;
}

bool DivergentPointersGroups::createAddNewGroups(const DivergentPointer &DP) {
  CommonBaseGroup Group = {};
  Group.DivergentPointers.push_back(DP);
  for (auto &IT : DP.Geps) {
    BasicBlock *BB = IT.first;
    AddrSpaceCastInst *ASC = IT.second.Cast;
    GetElementPtrInst *GEP = IT.second.GEP;

    if (GEP->getNumIndices() < 1)
      return false;

    SmallVector<Value *, 4> Indices(GEP->idx_begin(), GEP->idx_end() - 1);
    Value *PtrOperand = GEP->getPointerOperand();
    Type *PtrOperandTy = GEP->getSourceElementType();
    Group.GroupFactor[BB] = std::make_pair(std::make_pair(PtrOperandTy, PtrOperand), Indices);
    Group.Casts[BB] = ASC;
  }
  Group.Successor = DP.Phi->getParent();
  PointerGroups.push_back(Group);
  return true;
}

void DivergentPointersGroups::add(const DivergentPointer &DP) {
  // Check all GEPs without last index have the same type
  SmallVector<Type *, 2> Types;
  for (const auto &IT : DP.Geps) {
    GetElementPtrInst *GEP = IT.second.GEP;
    SmallVector<Value *, 2> IdxList{GEP->idx_begin(), GEP->idx_end() - 1};
    auto Type = GetElementPtrInst::getIndexedType(GEP->getSourceElementType(), IdxList);
    Types.push_back(Type);
  }
  auto predicate = [&Types](Type *T) { return T == Types[0]; };
  if (!std::all_of(Types.begin(), Types.end(), predicate))
    return;

  if (!addToExistingGroup(DP))
    createAddNewGroups(DP);
}

static Value *getLastIdx(GetElementPtrInst *GEP) {
  if (GEP->getNumIndices() == 0)
    return nullptr;

  auto IdxIt = GEP->idx_end() - 1;
  return IdxIt->get();
  ;
};

static ConstantInt *getCommonConstantOffset(const DivergentPointer &DP) {
  SmallVector<Value *, 2> LastIndices;
  for (auto &IT : DP.Geps) {
    GetElementPtrInst *GEP = IT.second.GEP;
    LastIndices.push_back(getLastIdx(GEP));
  }

  auto IB = LastIndices.begin();
  auto ConstantOffset = dyn_cast<ConstantInt>(*IB);
  if (ConstantOffset == nullptr)
    return nullptr;

  for (auto II = IB + 1, IE = LastIndices.end(); II != IE; II++) {
    auto CI = dyn_cast<ConstantInt>(*II);
    if (CI == nullptr)
      return nullptr;

    if (CI != ConstantOffset)
      return nullptr;
  }

  return ConstantOffset;
}

static bool sinkCommonOffsetForGroup(const CommonBaseGroup &Group) {
  // Find pointers with common constant offset
  SmallVector<std::pair<DivergentPointer, ConstantInt *>, 2> PointersToSink;
  for (auto &Pointer : Group.DivergentPointers) {
    auto ConstantOffset = getCommonConstantOffset(Pointer);
    if (ConstantOffset == nullptr)
      continue;

    PointersToSink.push_back(std::make_pair(Pointer, ConstantOffset));
  }

  // If pointers to split and sink are less than 2 than do nothing
  if (PointersToSink.size() < 2)
    return false;

  SmallVector<std::pair<Value *, BasicBlock *>, 2> NewPointers;
  bool NewGEP = false;
  Type *PhiElType = nullptr;
  // Create GEP for the common base in every basic block
  for (auto &IT : Group.GroupFactor) {
    BasicBlock *BB = IT.first;
    Type *PtrOperandTy = IT.second.first.first;
    Value *PtrOperand = IT.second.first.second;
    auto BaseIndices = IT.second.second;

    Value *NewPointer = PtrOperand;
    if (NewPointer == nullptr)
      return false;

    // If we have gep(A, constant) just take pure A without creating new GEP
    auto NewPointerElType = PtrOperandTy;
    if (BaseIndices.size() > 0) {
      auto BaseGEP = GetElementPtrInst::Create(PtrOperandTy, PtrOperand, BaseIndices, "", BB->getTerminator());
      NewPointer = BaseGEP;
      NewPointerElType = BaseGEP->getResultElementType();

      NewGEP = true;
    }

    if (auto ASC = Group.Casts.find(BB)->second) {
      auto PType = PointerType::get(NewPointerElType, ASC->getDestAddressSpace());
      auto BaseASC = new AddrSpaceCastInst(NewPointer, PType, "", BB->getTerminator());
      NewPointer = BaseASC;
    }
    PhiElType = NewPointerElType;
    NewPointers.push_back(std::make_pair(NewPointer, BB));
  }

  // Create and fill new phi node for base GEPs
  auto PhiType = NewPointers.front().first->getType();
  auto BasePhi = PHINode::Create(PhiType, 2, "", Group.Successor->getFirstNonPHI());
  for (auto &NP : NewPointers)
    BasePhi->addIncoming(NP.first, NP.second);

  // Create offset GEPs
  for (auto &IT : PointersToSink) {
    ConstantInt *Offset = IT.second;
    PHINode *PN = IT.first.Phi;
    auto Geps = IT.first.Geps;

    SmallVector<Value *, 4> Indices;
    if (NewGEP)
      Indices.push_back(ConstantInt::get(Offset->getType(), 0));
    Indices.push_back(Offset);

    auto OffsetGEP = GetElementPtrInst::Create(PhiElType, BasePhi, Indices, "", BasePhi->getNextNonDebugInstruction());

    bool isInBounds = false;
    for (const auto &Gep : Geps)
      isInBounds |= Gep.second.GEP->isInBounds();
    OffsetGEP->setIsInBounds(isInBounds);

    PN->replaceAllUsesWith(OffsetGEP);
  }
  return true;
}

static bool sinkCommonOffset(const std::vector<DivergentPointer> &DivergentPointers) {
  DivergentPointersGroups Groups;
  for (auto &DP : DivergentPointers)
    Groups.add(DP);

  bool changed = false;
  for (auto &Group : Groups.getGroups())
    changed |= sinkCommonOffsetForGroup(Group);

  return changed;
}

bool SinkCommonOffsetFromGEP::runOnFunction(Function &F) {
  bool changed = false;
  for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {

    // Collect phi node pointers for basic block
    auto DivergentPointers = findDivergentPointers(&(*BB));

    // Does not make sense operate with less than 2 divergent pointers
    if (DivergentPointers.size() < 2)
      continue;

    changed |= sinkCommonOffset(DivergentPointers);
  }
  return changed;
}
